The present invention relates to a spoke wheel for a tubeless tire and, in particular, a tubeless tire for motorcycles and similar vehicles.
Spoke wheels, which are wheels having a plurality of detachable spokes connecting a rim to a hub, have been in use for a long time. However, spoke wheels have not achieved a large acceptance, primarily because of problems in their design. For example, a spoke wheel designed to be sturdy (i.e., have a high resistance to radial and tangential stresses received from a tire, and a high resistance to stresses received from the spokes), but also light and easy to manufacture is particularly difficult to achieve. These difficulties have become magnified since the introduction of tubeless tires. This is due to the fact that the spokes, whether or not they are provided with fastening nipples, may create problems with the airtight seal of the tire when received in mounting holes provided in the well of the rim.
One type of spoke wheel which is specifically designed for tubeless tires is disclosed in Utility Model DE-GM 1718046. This spoke wheel has a rim having lateral flanges for retaining a tire. The rim is also provided with cantilevered extensions which protrude outward from the lateral flanges. These cantilevered extensions are adapted to receive an end of each of the spokes, preferably the end provided with a fastening nipple. Although these spoke wheels have a unique visual aspect due to the cantilevered extension, the wheel is not very sturdy unless high grade and very expensive metal alloys are used. This is because the stresses received from the spokes are carried by cantilevered and relatively weak portions of the rim.
Another, more recent, example of a spoke wheel for tubeless tires in disclosed in patent EP-B-0 143 394. The rim for a spoke wheel of this type is illustrated in FIG. 1, which shows a cross section of the wheel in a radial plane of the rim. Reference to this figure provides a useful comparison for the present invention.
Rim 1 for this spoke wheel has a profile conforming to European Tire and Rim Technical Organization (ETRTO) standards. Rim 1 comprises a pair of flanges 2, 3 abutting against beads of an outer side of a tire T, a pair of associated base walls 4, 5 which are adapted to carry the inner circumference of the beads, and a well 6 connecting the base walls 4, 5 to one another. Flanges 2, 3 must have a very large thickness so that a plurality of bore holes 9, which extend obliquely from the center plane P of the wheel, can be drilled in the flanges 2, 3. These bore holes 9 are for mounting therein end 7 (which has no nipple) of each of the spokes 8. The spokes 8 extend in a rectilinear direction to a ring-like extension of a concentric hub, and are fastened to the hub extension by nipples screwed at their second end (not shown). This spoke wheel may have some increased sturdiness. However, the wheel is markably heavy and may consequently have an undesirably high cost.
Another spoke wheel is disclosed in published Japanese patent abstract JP 60 259501. This reference discloses a spoke wheel including a rim having a main body, a pair of ear portions, and a pair of hollow portions provided on each side of the main body. Each of the ear portions include several throughholes which pass through the ear portions in a lateral (sideways) direction. In other words, the throughholes have a longitudinal axis that is substantially perpendicular to the longitudinal axis of each spoke which connects the rim to a wheel hub. Consequently, fastening the rim end of the each of the spokes to the rim is not easy due to the orientation of the throughholes. Moreover, because of the orientation of the throughholes, the rim ends of each of the spokes may contact the outer surface of the beads of a tire installed on the rim. Hence, the ends of the spokes may cause damage to the tire.